Royer Mod using MXL603S

[usekgb]

I'm just wrapping up a build of a Royer tube mic using an MXL 603S microphone.  My voltages are a touch on the high side, due to the Avel-Lindberg transformer I used putting out too high of a voltage.  The voltages are, however, within a reasonable tolerance, to I am going with it.  I though I would share a few pictures while I'm waiting for the output transformer to arrive.

The first picture is laying out the turret board:

 

[usekgb]

Power jack, transformer, switch, and circuit installed:

 

[usekgb]

5-pin XLR installed.  When I measured the voltages without the microphone attached, they were extremely high!  I was worried that I had done something horribly wrong.  After attaching the mic, the voltages fell down to reasonable operating levels.

 

[usekgb]

UPS says that my Cinemag output transformer will arrive sometime tomorrow by the end of the day.  I can't wait to button this thing up and use it in a session!!!

 

[pH]

Nice looking turret construction!
Be sure to try it on an electric guitar cab, it's become one of my favorite mics for that.

Paul

 

[usekgb]

Will do.  Do you prefer it on clean, dirty, or both?

 

[pH]

Both. Nice thing about this mic is that because it's a cathode follower it can handle a ton of gain and still sound detailed.

 

[usekgb]

Argh.....  Shipping on the output transformer delayed by a day.  Guess I'll have to wait 'till tomorrow to button this up.

 

[usekgb]

So I got this all put together (no pics yet) with a Cinemag CMMS-3 on the output, and I'm having some hum problems.  I mounted the output transformer right next to the xlr output on to a small sub-pcb, keeping the transformer wires very short.  From there, I used foil shielded belden solid mic cable to the output.  One thing that concerns me is, I'm hearing hum from the power transformer.  It is rated for 1 amp, so I shouldn't be stressing it.  Any ideas?

 

[usekgb]

Just to clarify, I'm actually hearing the power transformer hum when I put my ear near it.

 

[pH]

Many of my power transformers have some mechanical noise. The enclosures they're mounted in can make this worse by resonating.

Is there hum in the audio? It looks like the power and output transformers may be very close, many of us have put them in separate enclosures to keep the audio quiet.

 

[usekgb]

Yes, there is hum in the audio.  It got better when I mounted the output transformer on to a small pcb and shortened the wires.  The hum does not seem to change as I rotate the transformers.  My ground is a solid 14ga copper wire running along one side of the turret board, and terminated to the chassi at the same point I terminated the ground for the IEC plug.  I've used this grounding technique before without any problems.  I'm about ready to just use a 24v ac wall wart for this thing.  I really need it for a session, and the delays are frustrating.  The output transformer is as far away as it can physically be in this enclosure.

 

[pH]

The output transformer is as far away as it can physically be in this enclosure.

Your enclosure is too tight for enough separation between the power and the audio. I've seen some put a shield in larger boxes and get away with it, but in your case I think you'll have to move the PT to it's own case (or a wall wart). You'll be happy then 

 

[usekgb]

I will try some shielding first, but I think you are right.  I may just have to go with the wall wart.  :-[.  Such a shame too.  The enclosure looks pretty sweet.

 

[usekgb]

When I flip off the power switch, the mic sounds absolutely fabulous......  for about 15 seconds while the caps discharge.  ;D

 

[usekgb]

I tried shielding the power transformer, but no luck.  I finally rigged up a power transformer outside the enclosure (alligator clips and flying leads.  Not OSHA approved!) and the mic is dead quiet.  Looks like I either need to find a larger enclosure or just go with an external transformer.

As for the sound of this mic.....  I am really quite pleased.  I went with the Cinemag CMMS-3 instead of the Jensen transformer for no particular reason other than I've always been very happy with Cinemag stuff.  My acoustic guitar sounds wonderful through this mic.  It displays none of the harshness that the MXL mics are known for.  It's definitely a keeper!

 

[bruce0]

I tried shielding the power transformer, but no luck.  I finally rigged up a power transformer outside the enclosure (alligator clips and flying leads.  Not OSHA approved!) and the mic is dead quiet.  Looks like I either need to find a larger enclosure or just go with an external transformer.

As for the sound of this mic.....  I am really quite pleased.  I went with the Cinemag CMMS-3 instead of the Jensen transformer for no particular reason other than I've always been very happy with Cinemag stuff.  My acoustic guitar sounds wonderful through this mic.  It displays none of the harshness that the MXL mics are known for.  It's definitely a keeper!

This works.

Here is the little converter box, that has the transformer in it.  In Dave Royers original design this transformer was in the power supply enclosure.  By taking it out of the enclosure, yøu can worry less about shielding, and you can use the SAME power supply for the LDC and SDC Royermod mics (but on the SDC mic's you need to use this little interface box.) 

 

[usekgb]

That is a great idea!  So, the little box only contains the output transformer?

 

[bruce0]

That is a great idea!  So, the little box only contains the output transformer?

Looking back at the schematic and trying to remember, I think it holds C8, R5, and the transformer. I did it on a protoboard.

Another part as I remember was to change the 5 pin plug pin assignments so that if some idiot (that would be me) plugs the SDC mic in without the little transformer box, that nobody gets hurt. 


The box plugs into the normal Royermod LDC psu


It is very convenient to only have one type of Royer PSU.

 

[usekgb]

Very cool.  I'll keep that in mind.  I've got a couple LDC's that I was thinking of converting, and that would be a good cost/time saver for those.